Interpolyesters from aromatic dibasic acids and omega-hydroxyalkyl esters of carbonic acid



. at about 150 support or for textile fibers.

.alkyl diester of carbonic acid INTERPOLYESTERS FROM AROMATIC DIBASIjCACIDS AND OMEGA-HYDROXYALKYL ESTERS F CARBONIC ACID John R. Caldwell,Kingsport, .Tenm, assignor to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey No Drawing. Application July Serial No.445,935

19 Claims. (CL. 260-75) This application relates to valuable linearpolyesters prepared by condensing an aromatic dibasic acid diester andan omega-hydroxyalkyl diester of carbonic acid with with variousomega-hydroxyalkyl diesters of carbonic acid as well as certain othercompounds.

Highly polymeric esters of terephthalic acid and various. glycols, forexample, ethylene glycol, trimethylene glycol, hexamethylene glycol,etc., are well known, and have been used in the preparation of linear,highly polymeric polyesters having properties including that of be ingcapable of being formed into useful filaments, fibers and the like, andhaving high melting points and a low degree of solubility in organicsolvents. Linear polyesters prepared from other aromatic dicarboxylicacids have also been described in the prior art and contemporary art.Moreover, interpolyesters of terephthalic acid and other dibasic acidscondensed with dihydroxy compounds have also been described.

In most cases the known polyesters prepared from the aromatic dibasicacidssuch as terephthalic acid have sharp melting points. In contrast,the polyesters of this invention soften over a relatively widetemperature range and have exceptionally good flow characteristics, bothof which make these polyesters especially valuable for the production ofshaped objects by injection molding and extrusion methods. Moreover,thesepolyesters soften C. or higher. Those softening above 200 C. areespecially valuable. They can be advantageously employed for making manyshaped objects, and can be used in some instances as a, photographicfilm Fibers which can be produced from the higher melting polyesters ofthis invention are strong, elastic, and have exceptionaldyeability,

probably because the carbonate radical produces noncrystalline areas inthe polymer'whichare more readily penetrated by the dye. Furthermore,these polyesters are useful in making goodelectricalinsulating'materials.

According to my invention I have found. that certain aromatic dibasicacid vdiesters plus an omega-hydroxycan be condensed with apolymethylene glycol and possibly some aliphatic ether glycol orbranched chain glycol to producea new kind of linear interpolyesterhaving highly =valuableproperties which are superior in certain respectsto those of the linear polyesters described in the prior art.

nited States Patent deleterious effect on .groupcontaining from 1 to 6My novelinterpolyesters may contain as constituents thereof smallpercentages of the aliphatic ether glycols or branched chain alkyleneglycols without significant the properties of these interpolyesters. Infact, when the interpolyester is to be employed for purposes other thanfor making fibers, appreciable quantities of those added glycols can beemployed with some advantageous results as long as an exceptionally highmelting point is not desired.

Photographic film made from an interpolyester of this invention retainsits original dimensions to a very high degree despite the effects ofchanges in the humidity of the atmosphere, the treatment of the filmwith developing solutions, etc. The improvement is surprisingly great Iin comparison to conventional film made with cellulose of this inventionare their excellent dimensional stability and low degree of waterabsorptivity. This results in superior resistance to'dimensional changedespite changes in atmospheric humidity or immersion in aqueoussolutions.

One embodiment of this invention relates to a process .for preparing aninterpolyester comprising (A) condensingfrom aboutl to about 10 moleproportions of an aromatic dibasic acid diester having the followingformula:

wherein Ar represents a divalent radical selected from the groupconsisting of 1,4-disubstituted benzene, l,2-di- (p-substituted phenoxy)ethane, 1,2-di(p-substituted phenyl)ethane, p,p -disubstituted biphenyland 1,5-disubsti tuted naphthalene, and R1 and R2 each represent .aradical derived from an alcohol selected from the group consisting ofalkanols and polymethylene glycols contain ing up to 10 carbon atoms,plus one mole proportion of an omega-hydroxyalkyl diester of carbonicacid containing from 5 to 21 carbon atoms, (B) with a polymethyleneglycol containing from 2 to 10 carbon atoms, the polymethylene glycolbeing employed in such a proportion that there is at least an equivalentamount of oxy substituents in proportion to the carboxy substituents in.the overall combination of the diesters and the glycol, (C) in thepresence of a catalytic condensing agent, e. g. ,a compound selectedfrom the group consisting of thealkali metals, the alkaline earthmetals, the oxides of these two .groups of metals, the alkoxidescontaining from 1 .to 6

wherein M represents an alkali metahM' represents an alkaline earthmetal selected from the group consisting of magnesium, calcium andstrontium, R represents an alkyl carbon atoms,I R, and R' eachrepresents a membervof the group consisting of R and an aryl group ofthe benzene series containingfrom in such a proportion that about 2 oxysubstituents in proportion to the carbalkoxy from about 170'to about 2006 to 9 carbon atoms and Hal represents a halogen atom, (D) at anelevated temperature, (E) the condensation being conducted in an inertatmosphere, and (F) the latter part of the condensation being conductedat a very low pressure of the inert atmosphere.

Advantageously, the polymethylene glycol is employed there are fromabout 1.25 to substituents in the overall combination of the diestersand the polymethylene glycol. Advantageously, the low pressure definedunder (F) is less than about 15 mm. of

Hg pressure. Advantageously, the elevated temperature employed duringthe earlier part of the condensation is C. Advantageously thetemperature during the latter part of the reaction is from about 240 toabout 300 C., depending upon the melting point of the polyester.

The polymethylene glycols mentioned above may not .actually contain anyfree hydroxy radicals since they may bein esterified form. Whether ornot it is esterified, it is considered that the polymethylene glycolscontain 2 oxy substituents and no carboxy radicals which can enter intothe polyesterification condensation. Similarly, the omegahydroxyalkyldiesters of the aromatic acid or carbonic acid are each considered ascontaining 2 carboxy and 4 oxy substituents. Whenever the alcoholicportion of such esters is derived from a monohydric alcohol it isconsidered that the ester contains no oxy radicals and 2 carboxyradicals since the monohydric alcohols do not enter I into thepolyesterification reaction.

It is apparent that the process of this invention can be preceded by theformation of the aromatic dibasic acid diester by a preliminary stepcomprising condensing the free acid with a monohydric alcohol or morepreferably with a glycol.

glycol, etc. As indicated above, mono or diesters of these glycols canalso be employed. Thus, the acetates, propionates and butyrates areexamples of such esters. Mixtures of alkylene glycols or ether glycolscan also be employed. Examples of ether glycols include diethyleneglycol, triethylene glycol, tetraethylene glycol, bis(4-hydroxybutyl)ether, bis(3-hydroxypropyl) ether, etc. When 'mixtures of alkyleneglycols and ether glycols are employed, a major proportion of thealkylene glycol is employed in order to obtain higher melting linearpolyesters. The high melting characteristic also is dependent upon theamount of carbonic acid present in the interpolyester and the chainlength of the alkylene glycol employed.

Higher proportions of carbonic acid lower the melting and softeningtemperatures of the interpolyesters. The same effect is created byemploying a longer chain (higher carbon content) alkylene glycol. Forexample, when an 8 to 10 carbon atom glycol is employed, practically noaliphatic ether glycol should be employed; whereas, when a 2-4 carbonatom glycol is employed the amount of ether glycol can be a fairlysubstantial proportion of the total quantity of glycols. In lieu of theether glycols, the branched chain alkylene glycols can be similarlyemployed, e. g. Z-methylpentanediol, 3-methyl-hexanediol, etc.

Valuable fibers having high melting temperatures can be prepared byemploying ethylene glycol and at least 3 mole proportions of thearomatic dibasic acid diester for each mole proportion of the carbonicacid ester.

The temperature at which polyesterification can be conducted isdependent upon the specific reactants involved in any given reaction. Ingeneral, the reaction mixture can be heated at from about 150-170 C. toabout ZOO-220 C. for from approximately two to three hours in an inertatmosphere (e. g. nitrogen or hydrogen); the mixture can then be heatedat from about 225240 C. to about 280310 C. in the same atmosphere forapproximately 1 to 2 hours. Finally, the pressure can be greatly reducedto form a vacuum (less than about 15 mm. of Hg pressure but preferablyon the order less than 5 mm. of Hg pressure) while the temperature ismaintained in the same range (about 240-300 these conditions areadvantageously maintained for approximately 4 to 6 additional hours.This final phase is advantageously carried out with good agitation underthe high vacuum in order to facilitate the escape of volatile productsfrom the highly viscous melt. The conditions can be varied considerablydepending upon the degree of polyesterification desired, the ultimateproperties sought, the stability of the polyester being produced, andthe use for which the product is intended.

The catalytic condensing agents which can be employed have beendescribed above. From about 0.005% to about 0.2% of such catalysts basedon the weight of the reactants being condensed can be employed. Higheror lower percentages can also be employed. Generally, from about 0.01%to about 0.06% of the catalytic condensing agent can be advantageouslyemployed based on the weight of the various diester being condensed.

It has been found that the type of catalyst used has a significantbearing upon the properties of the final product. Although most of thecatalysts cited in the prior art may be used, it has been found thatcertain novel catalysts give superior results. The aluminum and titaniumalkoxide complexes described in copending applications filed on October3, 1952, are especially valuable for the preparation of the polyestersdescribed here. Moreover, novel tin catalysts have also been found to beespecially effective. See Caldwell Serial No. 313,072, Serial No.313,078, Caldwell and Reynolds Serial No. 313,077, Wellman and CaldwellSerial No. 313,074, Serial No. 313,075 and Serial No. 313,076, andWellman Serial No. 313,073 for a further description of these especiallyadvantageous catalytic condensing agents. The titanium, tin, andaluminum compounds are preferred catalysts.

The reaction can be carried out in the presence or absence of a solvent.Inert, high boiling compounds, such as diphenyl ether, diphenyl, mixedtolyl sulfones, chlorinated naphthalene, chlorinated diphenyl, dimethylsulfolane, etc., can be used as the reaction medium.

It is important to exclude oxygen and moisture at all stages of thecondensation reaction. Inert atmospheres which can be advantageousemployed include nitrogen, hydrogen, helium, etc. Substantiallyanhydrous reactants can also be advantageously employed although this isnot essential, especially if any water is removed in the earlier stagesof the condensation.

As indicated above, the acidic constituents of the interpolyesters areemployed in the form of their diesters. The omega-hydroxyalkyl diesterscan be prepared as mentioned above by heating a polymethylene glycolwith the free acid, preferably employing an excess of the glycol. Theacid chlorides can be employed in some cases although the conditionsinvolved are generally substantially different.

Examples of the various aromatic dibasic acid diesters which can beemployed in accordance with the process of this invention include theethyl, propyl, n-butyl, secbutyl, isopropyl, see-amyl, n-hexyl,10-hydroxydecyl, 5- hy'droxyamyl, 2-hydroxyethyl, etc. diesters of anyof the named aromatic dibasic acids. It is not essential that these besymmetrical esters, for example the methyl ethyl diester can be employedof p,p'-diphenic acid or the pentyl hexyl diester of 1,5-naphthalenedicarboxylic acid can be employed. Other esters include the sec. butyldiester of 1,2-di(p-carboxyphenyl)ethane, the methyl diester of1,2-di(p-carboxyphenoxy) ethane; 'the hydroxypenta- 'methyleneoxydiester of terephthalic acid, etc.

.dibasic acid selected from the phthalic acid,l,2-di(p-carboxyphenoxy)ethane, 1,2-di(pnaphthalene.

.asqasao to. the.oarbonic*acid d-iester willdependupon the type. ofproduct desired. As the mole percent of thecarbonic acid in thepolyester is increased, the imelting point of the-product. is lowered.-When. short. chain .glycols such asethylene glycol andtetramethyleneglycol are .used,

.moreof thecarbonic acid. ester can beemployed without reducing themelting point of the product below. about 150 C. Whenhigher glycols.such aspentamethylene, hexamethylene, and octamethylene glycol areused, up to about mole proportions of the aromatic dibasica'cid diestercan be advantageously: employed in order to keep a fairly high melting:point.

:In general, thepolyesters'can be"convenientlyrprepared .i'byi firstcondensing in thetpresenceof a catalyst an alkyl "ester of carbonic'acidwithat least 2 moles-of a glycol .toform the omega-hydroxyalkyl diesterof carbonic acid.

The usual esterinterchange catalysts can be advan- Theomega-hydroxyalkyl diester of The products of this invention are linearinterpolyesters which possess favorable flow characteristics over'atemperature differential or range of about 5 to 20 C.

and which contain inthe interpolyester configuration a ratio of fromabout l'to about'lO of one of the follow- :ing' repeating units:

'toeach one of the following repeating units:

wherein Ar isthe decarboxylated nucleus of an aromatic group consistingof terecarboxyphenyl)ethane, p,p-diphenic acid and'1,5-dicarboxynaphthalene and p represents a positive integer of from 2to 10. Ar .can also bedefined as setrorthhereinabove, i. e. as adivalent radical selected from the group consisting of 1,4-disubstitutedbenzene, 1,2-di(p.-substituted phenoxy) ethane, 1,2-di(p-substitutedphenyl) ethane, p,p'-disubstituted biphenyl-and 1,5-disubstituted In thefirst examplegiven below, the hot barsticking temperature is referredto. The hot bar sticking test can be bn'efly described as follows: Apolyester fiber is placed .on the. flat surface of a heatedbar and aweight of 100 grams is applied to the fiber along a distance of & inchof. the fiber length. The contact surface of thisweight has a coatingofpolytetrafluoroethylene which actsas a .thermal insulator. 'Thefiberis allowed to remain in con tact with the bar under this Weight for oneminute. The minimum temperature at which the fiber adheres to the hotbar under these conditions is the sticking temperature as that term isemployed herein.

"This'invention can be further illustrated by the following examples; inaddition to these examples it is apparent that other variations andmodifications thereof can be adapted to obtain similar results:

Example 1.Dimethyl terephthalate, di( /8'-hy'dr0xy- -ethyl)carbonate,and ethylene glycol One. hundred and eighteengrams (1.0 mole). of ethylcarbonate and 186 g.' (3.0 moles) of ethylene glycol were placed in-a.distilling.fiask. equipped with a distilling col- .product wasplacedin ayreaction vessel equipped .withea short-instillation column,anstirrer, and anjinlet for puri- ."fie'dihydrogen. 'Seven hundred and76g. (4.0 moles) of .dimethyl terephthalate,,and 5 00. g. (8.0 molesyoiethylene glycol were added to the vessel. A solution of 0.5 g. sodiumtitanium ethoxide in 25 cc. ethyl alcohol was added :as acatalyst. "Themixture was stirred at 19- 200 C. in an atmosphere of purified hydrogen.Methyl alcohol distilled rapidly and the ester interchangewaspractically complete in 3 hours. The temperature was then raised to 250C. and held forl hour. A vacuum of 0.5 mm. was applied and stirring-wascontinuedfor .3-4 hours. A high-viscosity, colorless polyester wasobtained.

The molar ratio of terephthalic acid to carbonic acid in the polyesteris 4:1. The following properties show the relationship of this polymer.to polyethylene terephthalate:

(a) The polymerization was carriedoutat atemperature of 250 C.Polyethylene terephthalate must ,be prepared at a temperature of.270-280C.-in order to pre vent solidification. This shows that the meltingpoint was depressed by the presence of carbonate radicals'in themolecular chain.

(b) The product is soluble intrichlorethane at C. Polyethyleneterephthalate is not soluble under these conditions.

The product was-spuninto fibers by extruding the melt-through amulti-hole spinneret. The fibers had a tensile-strength of 3.2 gramsperdenier and elongation of 22%. They had excellent elastic recovery.They stuck to the hot bar at 215-220" C. The fibers could be dyedreadily with cellulose acetate dyes.

Example 2.-Dimethyl terephthalate, di(fl-hydr0xy ethyl) carbonate andethylene glycol The procedure described in Example 1 was repeated.except that only half as much-of the dimethyl terephthalate andethylene glycol were employed. This produced a polyester in which themolar ratio of terephthalic acid to carbonic acid is 2:1. Thisinterpolyester had a softening temperature in the range of 160-l70 C. It

Example 3.-Dimethyl terephthalate, di(gamma-hya'r0xy propyl) carbonateand trimethylene glycol One hundred and eighteen grams (1.0 mole) ofethyl carbonate and 228 g. (3.0 moles)-of trimethylene glycol wereheated in a vessel equipped with a distillation colvumn. -A solution of0.4g. lithium aluminum ethylate in 10 cc. ethyl alcohol was used ascatalyst.

The tempera- .ture wasraised to 160 C. during a period of 4 hours.

About 1.8 moles of ethyl aleoholdistilled. from the reaction mixture.This product, which was principally di(gamma-hydroxypropyl) carbonate,was employed as described in Example make a mixed polyester withterephthalicacid. The product had the composition 3.0 moles terephthalicacid-l-LO mole carbonic acid+4.0 moles trimethylene glycol. 'Itsoftenedover about a 10 .degree range at around: C. This polyester isespeciallytvaluable as a molding plastic. Filmscan be-cast fromsolutions in trichlorethane.

Example 4.Diethyl p,p'-diphenate, di(fi-hydr0xyethyl)carbonate.andethylene glycol This polyester was prepared by means of the proceduredescribed in Examples 1 and 2 except that the diethyl .ester .ofp,p-diphenic acid was employed instead of di- .methyl terephthalate.'fThe interpolyester produced had the following composition: 2 mols ofp,p'-diphenic acid+1 mol of carbonic acid plus 3 mols of ethyleneglycol. This interpolyester softened at 160-170 C. It was useful for thesame purposes as described in Example 2.

Example 5.1,S-dicarboxynaphthalene, di(delta-hydroxybutyl)carbonate andtetramethylene glycol This interpolyester was prepared as described inthe preceding examples except that difierent reactants were employed.The di(delta-hydroxybutyl)carbonate was prepared as described in Example1 except that tetramethylene glycol was employed instead of ethyleneglycol. In carrying out the condensation reaction to produce thepolyester two mols of the diethyl ester of 1,5- dicarboxynaphthalene and1 mol of di(delta-hydroxybutyl)carbonate were reacted with 3.5 moles oftetramethylene glycol. The interpolyester produced had the followingcomposition: 2 moles of 1,5-dicarboxynaphthalene-l-l mole of carbonicacid+3 moles tetramethylene glycol. This product was suitable for thesame purposes as described in Example 3.

Example 6.-l,S-dicarboxynaphthalene, di(p-hydroxyethyhcarbonate andethylene glycol The procedure described in Example 5 was repeatedexactly except that ethylene glycol was employed instead oftetramethylene glycol. This interpolyester was useful for the samepurposes as was the product of Example 5. It had a higher softeningtemperature range. This product was especially suitable for injectionmolding.

Example 7.-1,2-di(p-carbethoxyphenoxy)ethane,di-(flhydroxyethyl)carbnate and ethylene glycol This polyester wasprepared according to the procedures set forth in the preceding examplesso as to produce a product having the composition: 6 moles of 1,2- di(pcarboxyphenoxy)ethane+1 mole of carbonic acid+7 moles of ethyleneglycol. This product was useful for the same purposes as describedabove.

Example 8.Dibutyl p,p-diphenate, di(delta-hydroxybutyl)carb0. zate andtetramethylene glycol This product was prepared as described in thepreceding examples whereby the interpolyester had the followingcomposition: 1 mole of p,p-diphenol ic acid+1 mole of carbonic acid+2moles of tetramethylene glycol. This product resulted in the formationof clear tough films when cast from a solution in tertiary clorethane.This interpolyester had similar properties to those described above.

Example 9.-1,Z-a'i(p-carbmethoxyphenyl)ethane,di(flhydroxyethyl)carbonate and ethylene glycol This product wasprepared as described in the preceding examples so as to result in thecomposition of: 4 moles of l,2-di(p-carboxyphenyl)ethane+1 mole ofcarbonic acid-l-S moles of ethylene glycol. This interpolyester hadessentially the same properties as those described above.

A polyester was Example 11.-Dihexyl terephthalate,di(delta-hydroxybutyl)carb0nate andtetramerhylene glycol This productwas prepared in the manner similar to that described in Examplel exceptfor the differences in the reactants. The polyester produced hadessentially portions of an aromatic dibasic acid diester having theformula:

wherein R1 and R2 each represents a radical selected from the groupconsisting of an omega-hydroxyalkyl radical containing from 2 to 10carbon atoms and an alkyl radical containing from 1 to 10 carbon atomsand Ar represents a divalent aromatic radical selected from the groupconsisting of 1,4-disubstituted benzene, 1,2-di- (p substitutedphenoxy)ethane, 1,2 di(p substituted phenyl)ethane, p,p'-disubstitutedbiphenyl and 1,5-disubstituted naphthalene, plus one mole proportion ofan omega-hydroxyalkyl diester of carbonic acid containing from 5 to 21carbon atoms, (B) with a polymethylene glycol containing from 2 to 10carbon atoms, the glycol being employed in such a proportion that thereis at least an equivalent amount of hydroxy substituents in proportionto the carboxy substituents in the overall combination of the diestersand the glycol, (C) in the presence of a catalytic condensing agent, (D)at an elevated temperature, (E) the condensation being conducted in aninert atmosphere, and (F) the latter part of the condensation beingconducted at a very low pressure of the inert atmosphere.

2. A process as defined in claim 1 wherein the elevated temperature isincreased gradually during the course of the condensation up to atemperature of from about 225 to about 310 C.

3. A process as defined in claim 2 wherein the condensing agent isemployed in an amount of from about 0.005% to about 0.2% based on theweight of the diesters employed.

4. A process as defined in claim 3 wherein the glycol is employed insuch a proportion that there are from about 1.25 to about 2 hydroxysubstituents in proportion to the carboxy substituents in the overallcombination of the diesters and the glycols.

5. A process as defined in claim 4 wherein the elevated temperatureemployed during the earlier part of the condensation is from about toabout 220 C. and the low pressure defined under (F) is less than about 5mm. of Hg pressure.

6. A process as defined in claim 5 wherein all materials employed in theprocess are substantially anhydrous.

7. A process as defined in claim 6 wherein the aromatic acid diester isdimethyl terephthalate, the carbonic acid diester is the hydroxyethyldiester and the glycol is ethylene glycol.

8. A process as defined in claim 6 wherein the aromatic acid diester isdimethyl terephthalate, the carbonic acid diester is the hydroxypropyldiester and the glycol is trimethylene glycol.

9. A process as defined in claim 6 wherein the aromatic acid diester isdiethyl p,p-diphenate, the carbonic acid diester is the hydroxyethyldiester and the glycol is ethylene glycol.

10. A process as defined in claim 6 wherein the aromatic acid diester is1,5-dicarbethoxy naphthalene, the carbonic acid diester is thehydroxyethyl diester and the glycol is ethylene glycol.

11. A process as defined in claim 6 wherein the aromatic acid1,Z-di(p-carbmethoxyphenyl)ethane, the carbonic acid diester is thehydroxyethyl diester and the glycol is ethylene glycol.

12. A process as defined in claim 1 wherein the arcmatic acid diester isformed by a preliminary step comprising condensing an aromatic dibasicacid selected from the group consisting of terephthalic acid,1,2-di(p-carboxyphenoxy)ethane, 1,2 di(p carboxypheny1)ethane,

p,p'-diphenic acid and 1,5-dicarboxynaphthalene with a polymethyleneglycol containing from 2 to 10 carbon atoms at an elevated temperature,after which preliminary step the carbonic acid diester and the glycolare added and the condensation is completed as described in claim 1.

13. A process as defined in claim 12 wherein the con densing agent isemployed in an amount of from about 0.005% to about 0.2% based on theweight of the diesters being condensed, the elevated temperatureemployed during the earlier part of the condensation to form theinterpolyester is from about 150 C. to about 220 C. and the low pressuredefined under (F) is less than about 5 mm. of Hg'pressure.

14. A linear interpolyester having a softening tempera ture range offrom about 5 to 20 C. containing in the interpolyester configuration aratio of from about 1 to about 10 of one of the following repeatingunits:

OOC-Ar-C0-0 CH2) pto each one of the following repeating units -O--CO-O(CH2) p where Ar represents a divalent radical selected from the groupconsisting of 1,4-disubstituted benzene, 1,2-di(p substituted phenoxy)ethane, 1,2-di(p-substituted phenyl) ethane, p,p-disubstituted biphenyland 1,5-disubstituted naphthalene, and p represents a positive integerof from 2 to 10, which interpolyester consists essentially of only thoserepeating units Whose formulas have been set forth in this claim andwhich interpolyester is capable of being readily formed into shapedobjects within its softening range.-

15. An interpolyester as defined in claim 14 wherein Ar represents1,4-disubstituted benzene and p represents 2.

16. An interpolyester as defined in claim 14 wherein Ar represents1,4-disubstituted benzene and 2 represents 3.

17. An interpolyester as defined in claim 14 wherein Ar representsp,p'-disubstituted bipenyl and 2 represents 2.

18. An interpolyester as defined by claim 14 wherein Ar represents1,5-disubsti-tuted naphthalene and p represents 2.

19. An interpolyester as defined by claim 14 wherein Ar represents1,2-di(p-substituted phenyl) ethane and p 20 represents 2.

References Cited in the file of this patent UNITED STATES PATENTSPeterson Aug. 6, 1940

1. A PROCESS FOR PREPARING A LINEAR POLYESTER COMPRISING (A) CONDENSINGFROM ABOUT 1 TO ABOUT 10 MOLE PROPORTIONS OF AN AROMATIC DIBASIC ACIDDIESTER HAVING THE FORMULA: